Several industries utilize conveyor and process belts for transporting loads from one location to another location or for passing loads through successive processing operations. Many of these applications require conveyor belts that are able to maintain cleanliness under various and sometimes harsh conditions. For example, in the food and dairy industries, conveyor belts should provide sanitary surfaces for conveying food and dairy products to minimize the potential for contaminating these products. To meet this need, conveyor belt surfaces are often formed of materials, for example thermoplastic materials, that do not become easily contaminated when contacted with food or dairy products on the conveyor belt surface.
Monolithic conveyor belts are often used in applications that require light to medium duty conveyor belts. Unlike traditional conveyor belts that include layers or plies of fabric carcasses embedded between thermoplastic or rubber layers, monolithic conveyor belts are typically formed from a single homogenous material, for example a thermoplastic material, although they may include other composite materials such as reinforcing fibers. Forming the belt from a single thermoplastic material is often desirable because the thermoplastic material is less prone to providing sites for microbiological growth due to contamination from, for example, contact with conveyed food or dairy products. However, because these monolithic conveyor belts do not include a fabric carcass to increase the tensile strength of the belt, it is particularly important to ensure that these belts possess a generally uniform cross sectional thickness, and do not have areas of weakness where tear propagation can occur, potentially leading to ultimate failure of the belt.
In addition, monolithic conveyor belts used in these applications can often take the form of positive drive belts. Like monolithic belts generally, as described previously, monolithic positive drive belts are formed of a homogeneous thermoplastic material, with or without the addition of reinforcing materials. However, these belts additionally include projections that are configured to interengage with structures on a drive roller to positively drive the projections to drive the conveyor belt. In one example, these belts include a series of equally longitudinally spaced, laterally extending drive projections or fins that extend generally orthogonally from the non-conveying surface of the belt. Unlike ordinary conveyor belts, which typically rely on friction between the belt and drive rollers in the conveyor system to provide the driving force to move the conveyor belt, positive drive belts utilize force generated on a driving side of the ribs, in addition to frictional forces, to generate the driving force to drive the belt. To this end, a conveyor system utilizing monolithic positive drive belts will typically include one or more driven rotatable sprockets that interengage with the ribs, so that upon rotation of the sprockets, the sprocket teeth will engage the driving side of the ribs to generate the driving force in the conveying direction of the conveyor belt system. Similarly, the positive drive belt may include cogs that are positively driven by a drive roller. Thus, monolithic positive drive belts typically have a uniform pitch, which is the longitudinal distance between the projections, e.g. the crests of the ribs along the belt, which corresponds to a uniform circular pitch of the sprocket being used to drive the belt.
During installation and repair of monolithic belts, including both standard and positive drive belts, it is often necessary to join together the ends of one or more monolithic conveyor belts. While several methods exist for joining together the belt ends, including utilizing adhesives or mechanical fasteners to join the ends, one preferred method is to form a butt weld between the belt ends. To this end, the belt ends are typically prepared by squaring the belt ends so that they extend orthogonally to the belt edges, although they may be formed at corresponding angles to one another. The prepared belt ends are heated to soften or melt the material at the belt ends. With the material in the belt ends remaining softened, the belt ends are subsequently urged together into end-to-end abutment so that the material of the two belt ends becomes intermixed. Upon subsequent cooling of the belt ends, the softened material of the two belt ends will harden and fuse to join the belt ends together.
Previous conveyor belt welders have generally included a pair of longitudinally extending belt positioning platens positioned side-by-side, with at least one of the platens translatable toward and away from the other platen. In this regard, it should be noted that this welder extends lengthwise across the lateral or transverse width of the belt so that the transverse center of the tool is generally disposed at the longitudinal ends of the belt or belts to be joined together.
The top surfaces of the platens are generally coplanar, and the belt ends are positioned on the platens, and held in place, so that upon lateral movement of one of the platens toward the other of the platens, the belt ends will engage to facilitate intermixing of the material of the belt ends. In the previous welders, a lever is connected to a shaft and configured so that rotation of the lever and the shaft generates transverse movement of one of the platens. A rack and pinion gear is used to translate the rotation of the shaft into transverse movement of the movable platen toward and away from the stationary platen.
In the prior welding apparatus, a contact heating element is positioned between the belt ends during heating, and the belt ends are moved into engagement with the contact heating element to melt the belt ends. The heating element includes an elongate contact heating bar or wand that has a pair of heated surfaces, on each side of an elongate bar with a generally rectangular cross section. A resistance heating element runs through the heating bar to heat the bar to a welding temperature. The heating bar is formed of a heat conducting material, for example a metal material, to conduct heat from the resistance heating element, to the outer heated surfaces of the heating bar. The heated surfaces face the belt ends to be welded together which are shifted to engage the heated surfaces for melting the belt material at the belt edges. Due to considerable material loss due to sticking of the belt material to the heated surfaces of the heating element, a non-stick material, for example Teflon, is coated on the heated surfaces to reduce the amount of material that sticks to the heating bar during contact heating of the belt ends.
In the prior welder, a handle is disposed at the top of the heating bar, to provide a location for a user to grasp and lift the heated bar from above in order to insert and remove the heated bar from its welding position between the belt ends. The handle is typically formed with a heat insulating cover to help protect operators from injuring themselves on the heated bar. The prior belt welder provides a space between the platens, between which the heated bar may be manually inserted and removed from above during welding.
Prior to use, the belt ends are typically prepared by cutting to form belt edges that are substantially perpendicular to the belt longitudinal or lengthwise direction. Next the belt ends are loaded on the platens. To this end, the user can rotate the handle, which causes the shaft to rotate, so that the pinion urges the rack laterally to move one of the platens toward and away from the other platen. To position the belt ends in a starting position, the user rotates the lever clockwise to space the platens apart. The user next places a separate spacer between the platens and rotates the lever in the opposite counter-clockwise direction to move the platen back toward the other platen to squeeze the platens against the spacer. The belt ends are next positioned on the platen upper surfaces. If the welder is being used to join positive drive belts ends, separate adapters must be utilized to key the ribs. The belt ends are clamped into position on the platen upper surfaces, with the belt ends positioned in end-to-end abutment, and the spacer is removed.
With the belt ends mounted, the user may next heat the belt ends by first rotating the lever clockwise to slide the movable platen away from the opposite platen, providing a space between the two belt ends. With the belt ends separated, the user must grasp the upper handle of the previously preheated heating bar, and manually lower the heating bar into the space between the belt ends. With the heating bar between the belt ends, the lever is rotated in the opposite counter-clockwise direction in order to move the movable platen back toward the opposite platen so that each belt end abuts a corresponding one of the heated surfaces of the heating bar to squeeze the heating bar between the belt ends. In the prior welder, the user visually determines the proper extent that the belt ends are moved against the heating bar and the amount of time that the belt edges are pressed against the heating bar by subjectively determining whether a sufficient mushroom shape of melted material has been extruded from between the belt ends and the heating bar. Thus, the user must determine, typically based on experience, the amount of time to leave the belt ends in engagement with the heated bar. The amount of time will generally depend on the characteristics of the belt, including its cross-sectional size and the material from which it is made, as well as the temperature of the heated bar. It should be noted that the material that is extruded from the belt ends during heating is not used to join the belt ends and must be removed. This can lead to inconsistent results welds because the extent of the mushroom of material is subjectively determined by the operator. This is particularly problematic in positive drive belts, because with varying amounts of extruded material, either the pitch will change between the adjacent ribs during joining of the belt ends or the amount of belt material at the joint will vary, leading to thinner areas of the belt with insufficient belt material and areas of weakness.
After the user has determined that the ends of the belt are sufficiently softened to form a weld therebetween, i.e. a sufficient mushroom of belt material has formed at the interface with the heating bar, the user must again rotate the handle in the clockwise direction to move the movable platen away from the stationary platen to provide clearance for removing the heated bar. With the belt ends separated the user again grasps the upper handle of the heating bar and lifts it from between the belts. While the belt ends are still softened, the user next rotates the handle back in the counter-clockwise direction so that the rack and pinion urge the movable platen toward the stationary platen to clash the belt ends against one another to overlap their softened material. In these systems, because it is important to quickly join the belt ends after they have been heated, the time required for the operator to remove the heating device has been found to reduce the quality of the resulting welds because the belt ends are given time to cool.
After the heating device is removed, the handle is rotated beyond the position at which the belts were loaded so that the belt ends overlap past their original position of end-to-end abutment and the softened material of the belts can intermix. In this regard, a portion of the melted material will be extruded from between the belt ends, forming a mushroom of material about the joint area. The extent that an operator moves the handle past the original end-to-end abutment with the prior welder is determined by the amount of material that extrudes out from between the belts, a subjective standard that does not provide consistent belt overlap distances from welding operation to welding operation, reducing the repeatability and quality of belt splices. It should be understood that at this point, the longitudinal lengths of the belt ends will be effectively decreased by a combined amount equal to the distance that the belt ends are overlapped beyond their original end-to-end abutment position. The belts are held in this position until the material between the belt ends is sufficiently cooled, to reharden, fusing the material of the two belt ends together and forming a joint between the two belt ends.
A high quality weld results in a joint between the belt ends that closely resembles the original belt in both material strength and size while also providing a continuous conveying surface. In contrast, poorly formed welds can result in bubbles forming in the material at the welding site due to overheating, potentially resulting in discontinuities in the belt surface providing locations for microbiological growth when contaminated and also areas of weakness where tear propagation and ultimate failure of the belt can occur. Poor welds can form for several reasons. For example, if the belt is heated at too high a temperature or for too long, the material at the very edge of the belt can become burned or overheated, changing the chemical composition of the material and potentially forming an area of weakness and discoloration of the belt and porous bubbles to form. If the belt ends are heated at too low of a temperature or for too short a period of time, the belt ends may not be sufficiently melted to intermix with the material of the opposite belt end to sufficiently fuse together to form a joint between the belts upon subsequent cooling.
Several problems have been found to exist with the prior welding tool that decrease the quality of welds produced with these tools. First, it has been found that during heating, with the belt ends contacting the resistive heating device, despite the non-stick coating on the heating bar, at least a portion of the heated material sticks to the heating element when the belts are removed. In addition, upon inserting and removing the heating element within the space between the belt ends, the operator often unintentionally contacts a portion of the heating element against a portion of the belt end, causing further material loss and non-uniform heating to the belt ends. Material sticking to the heating device is inconvenient to users and requires regular manual cleaning of the heating device between each welding operation. Material loss is also problematic, particularly if the welding tool is used to weld together ends of a positive drive belt. In this regard, it is difficult to maintain the pitch between ribs adjacent to the weld site, because an unknown quantity of the belt material is removed from the belt ends. Because the amount of overlap of the belt ends is determined by visually examining the extruded belt material between the belt ends as they are engaged, the extent to which the belts overlap to generate this material extrusion will vary with the amount of material lost during belt heating, decreasing the user's ability to obtain repeatable belt welding results and maintain the proper pitch between ribs of the belt. Because positive drive belts and the sprockets that drive them have precise corresponding pitches, altering the pitch between two ribs where the belt ends are joined together can interfere with proper functioning of the positive drive system. It has also been found that the edges of the belt ends contacting the heating element can become damaged or scorched during heating, degrading the quality of the final weld as described previously.
The prior welder can also lead to uneven belt heating and non-uniform belt joining results. More specifically, uneven heating can be caused if the heating element does not have a consistent temperature along the entire width of the conveyor belt ends so that hot and cool portions are formed with some material being subjected to more heat along the width of the conveyor belt. This can result in portions of the belt width becoming overheated or underheated, which may result in a deficient weld as described previously. In addition, it has been found that the prior welder leads to unrepeatable results due to the heating depth along the belt varying upon the user engaging the belt ends against the heating element. Specifically, determining that a proper mushroom shape of extruded material has formed between the belt ends and the heater to assess adequate heating is an imprecise measure and may vary from operator to operator and from weld to weld.
In the same manner, the extent that the user overlaps or clashes the belt ends together has been found to vary. During the belt joining stage, the user clashes the belt together until a proper “bead” of material forms at the interface between the belt ends at upper and lower surfaces thereof. However, determining the proper clash based on a bead of material forming is very subjective and makes it difficult for operators to generate repeatable results with consistent pitches of the resulting belt. In addition, the welding operation requires precision, with an amount of material clash on the order of one millimeter, so that it is difficult for an operator to provide the precise amount of rotation of the handle without moving the handle too much or too little, which can create a weaker weld because the material being clashed with the opposite belt end may be further from the edges of the belts, which may not be full melted, so that the resulting weld may be weak. Creating the wrong amount of overlap between the belt ends not only forms a weak weld between the belt ends but can also lead to an incorrect pitch between the ribs on a positive drive belt, decreasing its ability to properly operate in a positive drive system.
At the same time, the prior welder can be relatively unsafe and inconvenient because it requires the operator to rotate the handle with one hand while manually inserting and removing an extremely hot heating bar between the belt ends and an additional spacer. The operator must therefore go through a number of discrete steps and maintain the heating element outside of the tool for a substantial portion of the welding operation. In addition, the resistance heating elements used in this tool must be preheated for a relatively long period of time prior to reaching a desired weld temperature, and similarly must be cooled for a relatively long period of time, so that the cycle time for creating a weld can be long.
Another problem is that the monolithic belts can absorb moisture. When a monolithic urethane belt is exposed to moisture such as due to being submerged or simply being exposed to atmospheric moisture, a reaction between the urethane material of the belt and the absorbed water can take place during splicing leading to the undesirable formation of bubbles in the splice area. It has been recommended that the known, contact heater described above be used when condensation is present to preheat the belt. However, this process can take anywhere from approximately two to four hours further increasing cycle time for creating a weld.